Germanium-tin and silicon-germanium-tin layers have great applicability for optoelectronic applications. In particular, thick strain-free layers may be desired in various optoelectronic device architectures. Growth on lattice-mismatched substrates necessitates strain relaxation via dislocation formation in these layers. However, electronic and optical properties of the epitaxial layer are degraded by the presence of dislocations. As a result, a technique that allows for formation of a thick and dislocation-free epitaxial layer is desired.